1. Field of the Invention
The present invention relates to a power module in which a power switching semiconductor device is mounted on a circuit pattern formed on a front principal face of a power insulating substrate, a rear principal face of the power insulating substrate being bonded to an upper principal face of a base plate, an outer peripheral edge of the base plate being fixed to an open edge of one end of a cylindrical case, and a control substrate on which control components including a control semiconductor device for controlling the power switching semiconductor device are mounted, is disposed in the case while being opposed to the power insulating substrate with a gap therebetween, and more particularly to an improvement of electromagnetic shielding on such a control substrate.
2. Description of the Related Art
As a conventional power module of this kind, a power module for an automobile will be described with reference to FIG. 4.
Referring to the figure, 1 denotes a cylindrical case which has an opening at each of its ends, and 2 denotes a conductive base plate which is a copper plate, and which is fixed at an outer peripheral edge to the lower end of the case 1 so as to close the lower end opening of the case 1. The reference numeral 3 denotes a power insulating substrate in which a circuit pattern 3a is formed on the front principal face, and the rear principal face is bonded to the upper principal face of the conductive base plate 2, 4 denotes a power switching semiconductor device which is mounted on the circuit pattern 3a, and 5 denotes external power terminals which are inserted into the case 1, and one end of each of which is formed as an exposed face 5a on the inner side of a lower end portion of the case 1. The reference numeral 6 denotes bonding wires through which electrodes (not shown) of the power switching semiconductor device 4 are electrically connected, for example, via the circuit pattern 3a to the exposed faces 5a of the external power terminals 5.
The reference numeral 7 denotes a control substrate in which control components 8, such as a control semiconductor device for controlling the power switching semiconductor device 4, are mounted on the front principal face of the control substrate 7. An electromagnetic shielding plate 9 is integral with the rear principal face so as to shield the control components 8 from electromagnetic waves emitted from the power switching semiconductor device 4.
The reference numeral 10 denotes relay terminals through which a control signal from the control substrate 7 is transmitted to the power switching semiconductor device 4.
The reference numeral 11 denotes a wire harness comprising a grounding wire (not shown) through which the electromagnetic shielding plate 9 is electrically connected to a frame ground of an automobile, and wires (not shown) for input/output signals of the control substrate.
The reference numeral 12 denotes a gel-like resin which fills the case 1 so as to cover the front principal face of the power insulating substrate, the power switching semiconductor device 4, and the bonding wires 6, and 13 denotes a cover made of a resin which covers the other end opening of the case 1.
The reference numeral 14 denotes a heat sink which is attached to the lower principal face of the conductive base plate 2, and which is grounded.
Next, the operation of the thus configured power module of the conventional art will be described.
When a control signal which is supplied to the control substrate 7 through the wire harness 11 is turned on or off, the power switching semiconductor device 4 is turned on or off, so that the power which is supplied to a load through the external power terminals 5 is turned on and off, or, for example, PWM control is performed. A predetermined control signal is output through the wire harness 11.
When the power switching semiconductor device 4 is turned on and off, electromagnetic waves are generated. The electromagnetic waves are dissipated via the electromagnetic shielding plate 9 and the wire harness 11 to the frame ground of the automobile. Therefore, it is possible to prevent the control components 8 such as the control semiconductor device mounted on the control substrate 7, from being caused to malfunction by the electromagnetic waves generated by the power switching semiconductor device 4.
Unlike on the rear principal face of the control substrate 7, however, an electromagnetic shielding plate cannot be disposed on the front principal face of the control substrate 7 because the control components 8 are mounted on the front principal face. As a result, the control components 8, such as the control semiconductor device mounted on the control substrate 7, are sometimes caused to malfunction by external electromagnetic waves.
Since the wire harness 11 is used, the inductance of the wire harness 11 reduces the effect of the electromagnetic shielding against electromagnetic waves, whereby the control components 8, such as the control semiconductor device mounted on the control substrate 7, are sometimes caused to malfunction.
In a conventional art power module of this kind, control components, such as a control semiconductor device mounted on a control substrate, can be prevented from being caused to malfunction by electromagnetic waves generated by an incorporated power switching semiconductor device. However, such control components are not shielded from external electromagnetic waves, and hence there is a problem in that the control components sometimes malfunction and therefore the reliability of the power module is low.
The invention has been conducted in view of the above-discussed circumstances of the conventional art. It is an object of the invention to provide a power module which is not caused to malfunction by electromagnetic waves, and which therefore has high reliability.
It is another object of the invention to provide a power module which is not caused to malfunction by external electromagnetic waves, which therefore has high reliability, and which is compact in size.
It is a further object of the invention to provide an economical power module which is not caused to malfunction by external electromagnetic waves, and which therefore has high reliability.
The power module of the invention is a power module characterized in that an electromagnetic shielding member for shielding a control substrate from electromagnetic waves is disposed in a case, and the electromagnetic shielding member is electrically connected to a conductive base plate.
Front and rear principal faces of the control substrate may be covered with the electromagnetic shielding member.
Control components may be mounted on both of front and rear principal faces of the control substrate.
The conductive base plate and the electromagnetic shielding member may be electrically connected to each other by a conductive connecting member which is rigid, and the control substrate and the electromagnetic shielding member may be supported by the conductive connecting member.
The conductive connecting member may be inserted into the case.
The control components may be mounted on a front principal face of the control substrate, and a plate-like electromagnetic shielding member is disposed integrally on a rear principal face of the control substrate which is opposed to a power insulating substrate.